1. Field of the Invention
The present invention relates to a piezoelectrie ceramic material and a piezoelectric ceramic sintered body obtained using the same. The present invention particularly relates to a piezoelectric ceramic material that can be advantageously used for piezoelectricity application devices that are required to have a relatively small electromechanical coupling coefficient and a small resonant resistance, and a piezoelectric ceramic sintered body obtained using the same.
2. Description of the Related Art
Pb[(Mn.sub.1/3 Nb.sub.2/3), Zr, Ti]O.sub.3 based piezoelectric ceramic materials have been widely used for materials for constituting piezoelectric ceramic parts provided in piezoelectricity application devices including filters, oscillators and trap elements making use of bulk wave or surface wave because these materials have good resonance characteristics.
For example, Japanese Laid-open Patent Application No. 5-327397 discloses that a surface wave device having good resonance characteristics, temperature dependency of the resonance characteristics and heat resistance can be practically obtained by using a piezoelectric ceramic material represented by a general formula of (Pb.sub.1-x Me.sub.x){(Mn.sub.1/3 Nb.sub.2/3).sub.a Ti.sub.b Zr.sub.c }O.sub.3, wherein Me represents at least one of the element selected from Ca, Ba and Sr, and x, a and b satisfy the following relations:
0.005.ltoreq..times..ltoreq.0.10 PA1 0.0.ltoreq.a.ltoreq.0.14 PA1 0.40.ltoreq.b.ltoreq.0.60 PA1 0.26.ltoreq.c.ltoreq.0.59 and PA1 a+b+c=1.00
Japanese Laid-open Patent Application No. 5-24916 discloses {PbSr}{(TiZr)(MnNb)}O.sub.3 based materials containing at least one of 0.005 to 0.040% by weight of SiO.sub.2 and 0.005 to 0.040% by weight of Al.sub.2 O.sub.3 in which irregularity of electric characteristics has been improved.
Narrow-band filters of conventional Pb[(Mn.sub.1/3 Nb.sub.2/3), Zr, Ti]O.sub.3 based piezoelectric ceramic materials that are required to have a small electromechanical coupling coefficient cannot be designed in a saturation polarization state because the materials have a large electromechanical coupling coefficient in that saturation polarization state. Another problem is that filter insertion loss is increased due to increased resonant resistance when the degree of polarization is made to be in a saturated state for decreasing the electromechanical coupling coefficient.
Narrow-band filters are desired to be superior to wide-band filters in temperature stability of resonant frequencies. It is not possible for the conventional Pb[(Mn.sub.1/3 Nb.sub.2/3), Zr, Ti]O.sub.3 based piezoelectric ceramic materials to exhibit such excellent temperature stability as required for the narrow-band filters.